Method of fabricating a helical two-dimensional fiber sheet

ABSTRACT

A transverse fiber sheet is lapped by being guided in a substantially radial direction back and forth along a path between circumferentially outer and inner edges of the sheet, with the transverse sheet being reversed at each end of its path, the width of the transverse sheet being narrowed between the outer circumferential edge and the inner circumferential edge, the transverse sheet being held in place as it is lapped. Substantially mutually parallel yarns or tows are pulled to form a helical longitudinal sheet of density per unit area that decreases between its outer edge and its inner edge. The transverse sheet and the helical longitudinal sheet are superposed and advance continuously in flat rotation, and they are assembled together to form a helical two-dimensional sheet which is removed.

BACKGROUND OF THE INVENTION

The invention relates to fabricating a helical two-dimensional fibersheet.

A particular field of application of the invention is fabricatinghelical fiber sheets for making annular three-dimensional fiberstructures, such as reinforcing fiber structures for annular parts madeof composite material, in particular brake disks.

Brake disks made of composite material, in particular of compositematerial comprising carbon fiber reinforcement and a carbon matrix(carbon/carbon or C/C composites) or having a carbon fiber reinforcementwith a matrix that is at least in part made of ceramic (carbon/ceramiccomposites or C/C-ceramic composites), are well known. Fabricating themcomprises making an annular fiber preform and then densifying it with amatrix, densification being obtained using a liquid method (impregnatingwith a resin that constitutes a precursor for the matrix, followed bypyrolyzing the resin), or by a gas method (chemical vapor infiltration).

The fiber preform is usually made by stacking fiber plies and bondingthe plies to one another, typically by needling.

The annular shape of the preform may be obtained by cutting out from ablock made up of fiber plies stacked on one another and bonded together,or by stacking fiber plies that are of annular shape and that have beencut out from two-dimensional fabrics (woven cloth, one-directional ormulti-directional fiber sheets, felts, . . . ). This leads toconsiderable amounts of scrap material. The amount of scrap can bereduced by making plies that are annular by juxtaposing ring sectors cutout from a two-dimensional fabric, but that is at the price of animplementation that is more complex. Reference can be made in particularto the following documents: U.S. Pat. No. 4,790,052, U.S. Pat. No.5,792,715, and EP 0 232 059.

Methods have been proposed enabling an annular preform to be obtainedhaving the desired shape with practically no scrap material, suchmethods consisting in winding a helical fiber fabric with turns that aresuperposed flat, which turns are bonded to one another, in particular byneedling. Such methods making use of a deformable helical sheet or offlattened helical braids are described in particular in documents U.S.Pat. No. 6,009,605 and U.S. Pat. No. 5,662,855. Reference can also bemade to documents U.S. Pat. No. 6,363,593 and U.S. Pat. No. 6,367,130which relate to an installation for making such annular fiber preformsfrom helical two-dimensional fabrics.

Those methods for obtaining annular fiber preforms require helicalbraids or woven sheets to be made by methods that are relativelyexpensive.

Proposals have been made in document WO 98/49382 to make a thick annularfiber preform directly from free fibers without going via a step offabricating fiber fabrics, in particular by lapping a set of free fibersin the radial direction across a bed of disordered free fibers movedinto the circumferential direction, the fibers being bonded by needling.Apart from the fact that the description is practically silent about theway in which the bed of disordered fibers is made and the way in whichthe radial free fibers are deposited, it can immediately be seen that itis practically impossible to obtain a fiber preform that does notpresent a high degree of non-uniformity in thickness and in fiberdensity.

OBJECT AND SUMMARY OF THE INVENTION

An object of the present invention is to remedy the drawbacks of theprior art methods by proposing a method of fabricating a helical fiberfabric making it possible in particular to make thick annular fiberstructures in simplified manner and at relatively low cost, while alsominimizing the amount of scrap material and non-uniformities in densityand in thickness.

This object is achieved by a method comprising the following steps:

-   -   bringing at least one transverse fiber sheet and lapping it        while guiding it in a substantially radial direction along a        path in alternating directions between inner and outer        circumferential edges of the sheet, with the transverse sheet        being reversed at each end of its path, the width of the        transverse sheet being narrowed between the outer        circumferential edge and the inner circumferential edge;    -   holding the transverse sheet as it is lapped;    -   pulling a plurality of substantially mutually parallel yarns or        tows to form a helical longitudinal sheet with the density per        unit area of the longitudinal sheet decreasing from its        longitudinally outer edge to its longitudinally inner edge;    -   superposing the helical longitudinal and transverse sheets and        advancing them flat in continuous rotation;    -   assembling together the lapped transverse sheet and the        longitudinal sheet to form a helical two-dimensional sheet; and    -   removing the helical two-dimensional sheet formed in this way.

The method of the invention is remarkable in that it makes it possibleby a technique of the lapping type to obtain a two-dimensional sheetthat is helical. Manufacturing costs are lower than with weaving andbraiding techniques. The resulting helical sheet can then be useddirectly to obtain an annular fiber structure by superposing the turnsflat. The use of a sheet then makes it possible to reduce irregularitiesin thickness due to yarns crossing over, in comparison with fabrics thatare woven or braided.

The longitudinal sheet is preferably brought onto the lapped transversesheet immediately before the two sheets are assembled together, with theyarns of the helical longitudinal sheet thus being held in positionrelative to the lapped transverse sheet by the two sheets beingassembled together.

The transverse sheet may be made up of a plurality of yarns or tows orof at least one spread tow.

Advantageously, while the transverse sheet is being lapped it is guidedby passing over a guide so as to encourage narrowing of the sheet whilethe guide is moving from the outer edge towards the inner edge of thesheet, and vice versa.

Advantageously, the guide comprises two curved bars against which thetransverse sheet bears in alternation while the guide is being moved inone direction and in the opposite direction between the outer and inneredges of the sheet.

When the transverse sheet is made up of a plurality of yarns or tows,each yarn or tow is also guided between fixed guide elements extendingsubstantially radially between the outer and inner circumferential edgesof the sheet.

When the sheet is made up of at least one spread tow, the transversesheet is also preferably guided between two stationary guide elementsextending substantially radially between the outer and innercircumferential edges of the sheet.

In a variant, when the transverse sheet is made up of a plurality ofyarns or tows, each yarn or tow may be guided by passing through arespective yarn guide that is moved between the outer and innercircumferential edges.

Advantageously, after lapping, the transverse sheet is held, where itreverses, on supports situated along the outer and inner edges of thesheet, which supports are moved synchronously with the advance of thelapped transverse sheet and of the longitudinal sheet.

Retention may be provided in particular by suction on said supports orby passing around pegs carried by said supports.

The variation in the density per unit area of the helical longitudinalsheet may be obtained by using yarns or tows of different weights and/orby varying the spacing between the yarns or tows, whereas thelongitudinal yarns or tows may be pulled by passing them through a presscomprising two conical rollers pressing against each other.

Various means can be used for assembling together the longitudinal andtransverse sheets, such as needling, stitching with a bonding yarn, orinterposing hot-melt yarns.

The transverse and longitudinal sheets may be brought onto a stationaryannular support plate, which is advantageously in the form of a annularsector with a downstream end situated downstream from a zone forassembling together the longitudinal and transverse sheets, in thedirection of advance. The helical two-dimensional sheet is then removedfrom an outlet from the annular support plate that is situated at thedownstream end thereof. Advantageously, the helical two-dimensionalsheet as removed in this way is wound helically with turns that aresuperposed flat in a rotary annular storage drum situated beneath theannular support plate and having substantially the same axis as theplate.

In a variant, the lapped transverse sheet and the longitudinal sheet maybe brought onto a rotary annular support. The helical two-dimensionalsheet may then be removed laterally relative to the annular supportplate.

Another object of the invention is to provide an installation enablingthe above-defined methods to be implemented.

According to the invention, such an installation comprises:

-   -   an annular support plate;    -   a feed and transverse lapping device for moving a fiber sheet        transversely along a back-and-forth path from one side to the        other of the annular support plate with the transverse sheet        being reversed at each end of the path and with the sheet being        guided in a substantially radial direction;    -   means for holding the lapped transverse sheet;    -   a device for pulling a set of yarns or tows to form a helical        longitudinal sheet and for feeding it onto the annular support        plate;    -   a device for assembling together the lapped transverse sheet and        the longitudinal sheet to form a helical two-dimensional sheet;    -   means for continuously advancing the lapped transverse sheet and        the longitudinal sheet in flat rotation on the annular support        plate; and    -   means for removing the helical two-dimensional sheet after the        longitudinal and transverse sheets have been assembled together.

Advantageously, the device for feeding and lapping the transverse sheetcomprises a guide over which the transverse sheet passes, and means fordriving the guide in reciprocating motion along a substantially radialpath between the sides of the annular support plate, the guide beingmade in such a manner as to encourage narrowing of the transverse sheetwhile the guide is moving from the outside of the annular plate towardsthe inside, and vice versa. Also advantageously, the guide comprises twocurved bars against which the transverse sheet bears in alternation whenthe guide is moved in one direction and in the other direction betweenthe outer and inner sides of the annular plate.

When the transverse sheet is made up of a plurality of transverse yarnsor tows, the feeding and lapping device preferably further comprises aplurality of stationary guide elements disposed radially between theouter and inner sides of the annular plate and co-operating with thetransverse yarns or tows to guide each of them on its path between theouter side and the inner side of the annular support plate. However,when the transverse sheet is made up of at least one spread tow, thefeeding and lapping device preferably further comprises two stationaryguide elements disposed radially between the outer and inner sides ofthe annular support plate, and between which the transverse sheet isguided on its path between the outer side and the inner side of theannular support plate.

In a variant, when the transverse sheet is made up of a plurality oftransverse yarns or tows, the feeding and lapping device may comprise aplurality of yarn guides each associated with a respective transverseyarn or tow, and means for displacing the yarn guides back and forthalong substantially radial paths between the outer and inner sides ofthe annular support plate.

Advantageously, the means for holding the lapped transverse sheetcomprise supports in the form of bands or rings situated on either sideof the annular support plate, holding means for holding the transversesheet on said support where the sheet reverses, and means for drivingsaid supports synchronously with the advance means.

In an embodiment, the holding means comprise a suction chamberassociated with the supports in the form of bands or rings in order tohold the transverse sheet thereagainst by suction.

In another embodiment, the holding means comprise pegs carried bysupports in the form of bands, so as to enable the transverse sheet tobe reversed around the pegs.

The device for pulling the longitudinal sheet may comprise a pressformed by two conical rollers with the yarns or tows forming thelongitudinal sheet passing between them.

The device for assembling together the longitudinal sheet and the lappedtransverse sheet may be a needling device comprising at least oneneedling head and extending over an annular sector above the annularsupport plate, which is provided with perforations in register with theneedles of the needling device.

In a variant, the device for assembling the longitudinal sheet and thelapped transverse sheet together may comprise at least one stitchinghead for assembling the sheets together by means of a bonding yarn.

The advance means may comprise drive means for driving the helicaltwo-dimensional sheet in the advance direction, the drive means beinglocated downstream from the assembly device.

The annular support plate may be stationary and extends over an annularsector having a downstream end in the advance direction of thelongitudinal sheet and the lapped transverse sheet, said downstream endbeing situated downstream from the device for assembling the sheetstogether. In which case, the means for removing the helicaltwo-dimensional sheet may comprise an annular drum situated beneath theannular support plate and having substantially the same axis as thesupport plate, and means for driving the annular drum synchronously withthe advance means so that the helical two-dimensional sheet leaving theannular support plate from its downstream end is continuously collectedand wound in the drum.

The annular support plate may also be rotary, in which case it maypresent a top portion presenting a brush of rigid bristles.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the method of the invention will appearon reading the following description given by way of non-limitingindication and with reference to the accompanying drawings, in which:

FIG. 1 is a highly diagrammatic overall view in perspective of aninstallation for implementing a method of the invention;

FIG. 2 is a highly diagrammatic plan view of the FIG. 1 installation;

FIG. 3 is a fragmentary perspective view in greater detail showing howthe transverse yarns are fed and how they are held at the edges of thesheet of longitudinal yarns;

FIG. 4 is a diagrammatic view showing the orientations of the yarns ofthe transverse sheet after it has been lapped;

FIG. 5 is a fragmentary plan view showing diagrammatically how atransverse sheet made up of a spread tow is lapped on the sheet oflongitudinal yarns;

FIG. 6 is a fragmentary perspective view in greater detail showing howthe transverse sheet of FIG. 7 is lapped;

FIG. 7 is a fragmentary view in radial section on plane VII of FIG. 1showing in greater detail how the sheet of longitudinal yarns is fed inthe installation of FIG. 1;

FIG. 8 shows a variant way of making up the sheet of longitudinal yarns;

FIG. 9 is a fragmentary view in section on plane IX of FIG. 1 showinghow the longitudinal and transverse sheets are assembled together;

FIG. 10 is a view similar to that of FIG. 5 showing another way ofholding the transverse yarns at the edges of the sheet of longitudinalyarns;

FIG. 11 is a diagrammatic fragmentary perspective view showing how thehelical two-dimensional sheet is removed in the embodiment of FIG. 10;

FIG. 12 is a highly diagrammatic and fragmentary view showing a variantof the embodiment of FIGS. 10 and 11;

FIG. 13 is a diagrammatic plan view of another embodiment of aninstallation enabling a method of the invention to be implemented;

FIG. 14 is a more detailed fragmentary view in side elevation seenlooking along arrow XIV of FIG. 13;

FIG. 15 is a more detailed fragmentary view in section on plane XV ofFIG. 13, showing how the sheet of transverse yarns is lapped;

FIG. 16 is a detail view showing how the transverse yarns are held atthe edges of the longitudinal sheet in the installation of FIG. 13;

FIG. 17 is a detail view showing another way of holding the transverseyarns at the edges of the longitudinal sheet in the installation of FIG.13; and

FIG. 18 is a diagrammatic overall view in perspective of anotherembodiment of an installation enabling a method of the invention to beimplemented.

DETAILED DESCRIPTION OF EMBODIMENTS

In general (FIG. 1), a special installation enabling a method of theinvention to be implemented comprises a device 100 for forming atransverse sheet 102 lapped on a stationary horizontal annular supportplate 120, a device 200 for pulling and depositing a helical sheet 202made up of longitudinal yarns or tows 204 on the support plate 120, adevice 300 for assembling together the lapped transverse sheet 102 andthe longitudinal sheet 202 while they are on the plate 120, and a device400 for removing the resulting annular two-dimensional helical sheet 400from the plate 120 at the outlet from the assembly device. Thetransverse sheet and the longitudinal sheet deposited on the plate 120,and also the resulting two-dimensional helical sheet 402 are moved incontinuous rotation on the plate 120 about its center (arrow F). Driveis provided by a puller device 410 comprising a pair of conical rollers412 a, 412 b, at least one of which is motor-driven, situated downstreamfrom the assembly device, the two-dimensional helical sheet being pulledby passing between the rollers 412 a, 412 b which are pressed againsteach other.

Forming the Transverse Sheet

The sheet 102 is formed by lapping transverse yarns or tows 104 fed ontothe support plate 120. The plate 120 is in the form of a annular sectorof center O. By way of example, it is constituted by a smooth metaltable. The elements 104 are referred below as yarns for the sake ofsimplicity. The yarns 104 are preferably of the same weight and they arepreferably fed with the same mutual spacing.

The yarns 104 are of a material that is selected as a function of theuse for which the two-dimensional helical sheet that is to be made isintended. In an application to making reinforcing fabrics, or preforms,for C/C composite material parts or carbon/ceramic or C/C-ceramiccomposite material parts, the yarns 104 are commercially availablecarbon yarns such as 12K (12,000 filaments), 24K, 50K, or 80K yarns.

Each of the transverse yarns 104 forming the transverse sheet 102 istaken from a respective bobbin carried by a creel (not shown). The yarns104 arrive substantially parallel to one another at a guide frame 106.The yarns 104 are fed, e.g. substantially vertically over the middleradius of the plate 120 and they are deflected horizontally by the frame106.

The frame 106 is secured to a rod 110 which is moved horizontally backand forth in a radial direction under drive from a drive member such asan actuator (not shown). The frame 106 thus executes reciprocatingmotion in radial translation between an outer ring 130 and an inner ring140 extending along the outer and inner edges of the support plate 120,but forming complete rings around the center O.

The frame 106 is disposed substantially horizontally parallel to thesupport plate 120, and has two opposite sides formed by curved bars 108a, 108 b. While the frame 106 is being moved radially inwards, i.e.towards the inner ring 140 (or towards the inside edge of the transversesheet), the yarns 104 press against the convex profile of the bar 108 a,thus encouraging the sheet 102 to become narrower. Conversely, while theframe is moving radially outwards, i.e. towards the outer ring 130 (orthe outer edge of the transverse sheet), the yarns 104 bear against theconcave profile of the bar 108 b, thereby encouraging the sheet 102 tobecome wider. The bars 108 a and 108 b could be given different amountsof curvature corresponding substantially to the curvature of the rings140 and 130 respectively, or the same amount of curvature, e.g.corresponding to the mean curvature between the rings 140 and 130.

As shown in particular in FIGS. 3 and 7, the outer ring 130 isconstituted by a downwardly open channel-section bar whose top wall orweb 132 is provided with perforations 134. Similarly, the inner ring 140is formed by a downwardly channel-section bar whose top wall or web 142is provided with perforations 144. The rings 130 and 140 are turnedsynchronously with the advance of the sheet on the support 120, as isdescribed below. The surfaces of the webs 132, 142 and of the supportplate 120 are substantially coplanar.

A stationary suction chamber 150 (FIG. 3) of annular shape extendsbetween the flanges of the outer ring 130 over an annular sectorextending from an upstream end situated upstream from the zone in whichthe transverse yarns 104 are lapped to a downstream zone situateddownstream from the upstream end of the zone in which the longitudinaland transverse sheets are assembled together (where the terms “upstream”and “downstream” are used herein relative to the direction of advance ofthe two-dimensional sheet that is being formed).

The chamber 150 thus extends not only over the entire length of the zonein which the yarns 104 are lapped on and over the zone in which thelongitudinal sheet 102 is deposited, but also over at least a fractionof the assembly zone. The chamber 150 is defined by side walls adjacentto the flanges of the ring 130, a bottom wall, and end walls at itsupstream and downstream ends, and it is open on top in register with theperforated wall 132 of the ring 130.

In similar manner, a stationary suction chamber 160 of annular shapeextends between the flanges of the inner ring 140 over substantially thesame annular sector as the chamber 150. The chamber 160 is defined byside walls adjacent to the flanges of the ring 140, a bottom wall, andupstream and downstream end walls, and it is open in register with theperforated wall 142 of the ring 140.

The chambers 150 and 160 are connected to a vacuum source (not shown) bypipes 152, 162 that open out into the bottoms of the chambers.

A stationary guide comb 112 comprises a set of blades 114 which extendradially immediately above the support plate 120, and the rings 130 and140. On the inside, the blades 114 forming the teeth of the comb areunited by a strip 116 that is secured to a stationary support (notshown).

In operation, as the guide frame 106 moves towards the inner ring 140,the transverse yarns 104 are moved towards one another by sliding overthe curved bar 108 a while also being guided by the vertical side facesof the blades 114 of the comb 112. While the guide frame 106 is movingtowards the outer ring 130, the transverse yarns are moved apart fromone another by sliding on the curved bar 108 b, and while still beingguided by the vertical side faces of the blades 114 of the comb 112.Where they are turned around at the ends of the stroke of the guideframe 106, the transverse yarns are held by suction to the rotary rings130 and 140 on either side of the edges of the plate 120.

In the example shown, the guide 106 is moved immediately above the comb112. In a variant, the guide 106 may be moved in a space providedbetween the support plate 120 and the comb 112.

The transverse yarns 104 are lapped with continuous and synchronizedadvance of the lapped transverse sheet 102, of the longitudinal helicalsheet 202, and of the rings 130 and 140, so the transverse yarns 104 aredeposited in directions that are not radial, with the yarns 104 crossingover one another and also over the longitudinal yarns 104 (FIG. 1).

FIG. 4 shows an example of the way in which ten yarns are lappedtransversely. It can be seen that the angle between the lappedtransverse yarns varies, increasing from the outer circumferential edge(radius r₄) to the inner circumferential edge (radius r₁) of the sheet.The radius r₂ is the middle radius, while the line corresponding to theradius r₃ separates the annular sheet in two parts of same surface. Inorder to obtain a two-dimensional sheet that is as uniform as possible,it is advantageous to ensure that the transverse yarns cross so as toform an angle that is close or approximately equal to 60° at thecircumference of radius r₃ so that, at this position, the transverseyarns and the longitudinal yarns are oriented in a 3×60° configuration.This can be adjusted by varying the speed of advance of the sheet overthe support plate 120 and the speed at which the transverse yarns arefed for given dimensions of the helical sheet. In the example shown, theangle formed by the transverse yarns varies over the range 41° to 117°between the outer and inner circumferences, and it is equal to 58° atthe circumference of radius r₃.

FIGS. 5 and 6 show a variant embodiment of a transverse sheet 162 madeby lapping a spread tow 164. For this purpose, it is possible to use atow of high weight, e.g. a 300K, 320K, or 400K carbon tow. The tow maybe spread out in well-known manner by being passed over at least onecurved roller (or “banana” roller), not shown, with spreading possiblybeing assisted by exposure to a jet of air, as described for example indocument PCT/FR02/02249. It is possible to juxtapose a plurality ofspread tows in order to obtain a sheet of greater width.

The spread tow 164 passes through a guide frame 166 analogous to theabove-described frame 106, having two curves bars 168 a and 168 b. Onits path between the outer and inner rings 130 and 140, the tow 164 isalso guided between two stationary radial blades 174 carried by a strip176 on the inner side.

The guide frame 166 is moved radially back and forth. While it is movingradially inwards, it contributes by means of its bar 168 a and inco-operation with the stationary guide blades 174 to cause thetransverse sheet 162 to become narrower between the rings 130 and 140 soas to give it the shape of a annular sector. While it is moving radiallyoutwards, the guide frame 166 contributes, by means of its bar 168 bco-operating with the blades 174, to widening the transverse sheet 162again. The transverse sheet is held where it reverses direction bysuction against the rings 130 and 140.

Forming the Helical Longitudinal Sheet

The helical longitudinal sheet 202 comprises a plurality of mutuallyparallel longitudinal (or circumferential) yarns or tows 204 that aredrawn from respective bobbins carried by a creel (not shown). In thedescription below, the elements 204 are referred to as “yarns” forreasons of simplicity. The longitudinal sheet 202 extends over a widththat substantially equal to the width of the helical two-dimensionalsheet that is to be made.

In one embodiment (FIGS. 1, 2, and 7), the longitudinal yarns 204 are ofthe same weight and they are disposed with spacing between adjacentyarns that decreases between the inner longitudinal edge 202 a of thelongitudinal sheet (corresponding to the inside circumference of thehelical two-dimensional sheet that is to be made) and the opposite outerlongitudinal edge 202 b. The spacing between the yarns of thelongitudinal sheet is advantageously varied so that after assembly withthe transverse sheet, a density per unit area is obtained for thehelical two-dimensional sheet that is substantially constant across thewidth thereof.

In another embodiment (FIG. 8), longitudinal yarns 204′ are used thatare of differing weight, and that are disposed with constant spacingbetween adjacent yarns. The weight of the yarns varies, increasing fromthe inner edge 202 a to the outer edge 202 b of the sheet 202. The wayin which weight varies is advantageously determined so that afterassembly with the transverse yarns, density per surface area is obtainedfor the helical two-dimensional sheet that is substantially constantover the width thereof.

Naturally, it would also be possible to combine varying the spacingbetween the longitudinal yarns with varying the weights thereof.

The yarns 204 are of a kind similar to that of the yarns 104.

The yarns 204 are fed (FIGS. 1, 2, and 7) by means of a press 206 formedby two conical rollers 208 a, 208 b that press against each other. Atleast one of the rollers 208 a, 208 b is rotated to pull the yarns 204.The yarns 204 pass successively over the upper roller 208 a, between theupper roller and the lower roller 208 b, and then over the lower roller.The yarns 204 are delivered by the lower roller 208 b onto thetransverse sheet that has been lapped on the horizontal support plate120.

In order to impart the desired spacing between the yarns 204 of thesheet 202, they are passed over a spreader bar 110 (FIG. 7) upstreamfrom the press 206. Each yarn 204 passes through the bar 210 in arespective guide, e.g. an orifice made therein, a gap between two partscarried by the bar 210, or indeed a groove formed in the bar. Othermeans may be provided for adjusting the spacing between the yarns 204,e.g. a comb.

The increase in the density per unit area of the transverse sheet 102 or162 between the outer edge and the inner edge of the plate 120 iscompensated by varying the density of the longitudinal sheet in theradial direction so as to obtain a two-dimensional helical sheet ofdensity per unit area that is substantially uniform.

Assembling the Longitudinal and Transverse Sheets Together

The assembly that is displaced continuously and that is formed by thetransverse sheet as lapped and by the longitudinal sheet is brought tothe assembly device 300.

In the example shown (FIGS. 1, 2, 9) the assembly device comprises aneedling head 302 generally in the shape of a annular sector andextending between the edges of the support plate 120, above it. The head302 carries a plurality of needles 304 that are uniformly distributedand it is driven with vertical reciprocating motion under drive from acrank type drive member (not shown). The support plate 120 presentsperforations 128 in register with the needles 304 so as to enable themto penetrate through the plate without being damaged.

The needles 304 pass through the sheet 202 and 102 (or 162) bonding themtogether by tangling filaments from the yarns 204 and 104 (or from theyarns 204 and the tow 164).

It should be observed that bonding two fiber sheets together by needlingis well known in itself.

Suction at the edges of the lapped transverse sheet at the rings 130 and140 is maintained until the longitudinal and transverse sheets have beenassembled together sufficiently, for example at least halfway along theannular sector occupied by the needling head.

The helical longitudinal sheet 202 is preferably deposited on the lappedtransverse sheet 102 as close as possible to the upstream end of theassembly device 300, i.e. immediately prior to the sheets beingassembled together, so as to avoid possible displacement of the yarns204 in a radial direction, i.e. so as to conserve the relative positionsof said yarns in the sheet 202 since prior to assembly, the yarns 204are not held in place.

Nevertheless, it would also be possible to begin by depositing thelongitudinal sheet 202 and then lap the transverse sheet 102 on thesheet 202 on the plate 120.

The longitudinal and transverse sheets may be assembled together in waysother than by needling.

Thus, it is possible to perform assembly by stitching with a bondingthread. The assembly device then comprises a stitching head disposedradially, or a plurality of stitching heads spaced apart from oneanother across the width of the longitudinal sheet.

It is also possible to place hot-melt yarns on the transverse sheetprior to depositing the longitudinal sheet, with the assembly devicethen comprising means for heating the hot-melt yarns inserted betweenthe sheets.

Removing the Two-Dimensional Helical Sheet

The helical two-dimensional sheet 402 obtained at the outlet from theassembly device is pulled by the conical rollers 412 a and 412 b and iswound continuously into an annular drum 420 situated beneath the supportplate 120 and having the same axis as the support plate (FIG. 1).

The plate 120 in the form of a annular sector has a downstream end 124situated between the assembly device 300 and the puller device 410. Itsupstream end 122 is preferably situated upstream from the device 100 forlapping the sheet 102.

The annular drum 420 receives the sheet 402 which drops therein undergravity on leaving the puller device 410. The sheet 402 is wound in thedrum 420 as successive turns which are superposed flat by the drum 420rotating synchronously with the advance of the sheet 402 on the supportplate 120.

To this end, the drum 420 may be mounted on a turntable 422 driven by adrive roller or gear 424 mounted on a vertical drive shaft 426. Theshaft may also carry a drive roller or gear 428 for driving the outerring 130. The turntable 422 presents an axial rod 430 connected to theinner ring 140 by arms 432. Thus, the annular drum 420, the outer ring130, and the inner ring 140 are rotated together synchronously. Theouter ring 130 is supported by bearings (not shown) on which thevertical flanges of the ring are supported either by friction or viarolling bearings.

Other Embodiments

FIGS. 10 and 11 show an embodiment which differs from that of FIGS. 1 to3 and 7, 8 in particular in that the transverse sheet is held where itsyarns change direction on either side of the support plate 120 by theyarns passing around vertical pegs 135, 145 carried by the rings 130,140 (FIG. 10).

The rings are then constituted merely by annular bands withoutperforations and without associated suction means.

On leaving the assembly device 300 (FIG. 11), the resulting helicaltwo-dimensional sheet 402 is separated from the pegs 135, 145 by beingraised vertically upwards. For this purpose, the tangential line betweenthe rollers 412 a and 412 b of the puller device 410 is situated abovethe top end of the pegs. Separation of the sheet 402 may also beassisted by curving the downstream end portion 124 of the support plate120 upwards. The sheet 102 may be collected in an annular drum, as inFIG. 1, preferably with the edges of the sheet being guided until theyare beneath the plane of the rings 130, 140 so as to avoid interferencewith the pegs 135, 145 after it has been separated therefrom.

In a variant (FIG. 12), use is made of pegs 135, 145 that are verticallyretractable. The pegs pass vertically through the rings 130, 140 andtheir bottom ends are pressed against stationary cam paths 136, 146. Thecam paths 136, 146 are shaped in such a manner as to allow the pegs tobe retracted downwards as soon as they leave the assembly device 300,and enable the pegs to be raised subsequently on entering the upstreamend of the lapping device 100. It is then not necessary for the sheet402 to be moved upwards in order to be separated from the pegs forremoval purposes.

FIGS. 13 to 16 show another embodiment which differs from that of FIGS.1 to 3 specifically in the way the transverse sheet is lapped and theway in which the lapped transverse sheet is driven.

Each transverse yarn 104 forming the sheet 102 passes through a yarnguide 280 such as an eyelet moved back and forth in a radial directionbetween the inner and outer edges 120 a and 120 b of the support plate120. Each yarn guide 280 is secured to a support 282 that is guidedalong a horizontal radial rod 284. The support 282 is secured to a cord286 which is looped at the end of the rod 284 by passing over a drivingpulley 288 and a deflector pulley 290. The pulley 288 is drivenalternatively in one direction and in the opposite direction by means ofa motor (not shown). Other means for driving the support 282 could beprovided, e.g. actuator rods.

In the figures, only some of the transverse yarns and their associatedfeeder means are shown in order to clarify the drawings.

Each transverse yarn 104 is held on either side of the plate 120 bypressing against respective belts 180, 190. The belts 180, 190 areguided in horizontal slideways 182, 192 extending along and beyond theedges 120 a and 120 b of the support plate 120. In its bottom, eachslideway 182, 192 presents one or more slots or a plurality of holesconnected via couplings 184 to pipes 186, 196 connected to a vacuumsource (not shown). The pipes 186, 196 extend beneath the devices 100and 200 for feeding the transverse and longitudinal sheets, and alsobeneath at least a part of the assembly device 300.

The belts 180 and 190 are endless belts following respective horizontalpaths in the slideways 182, 192 between the upstream and downstream ends122 and 124 of the support plate 120.

The belt 180 passes over a drive wheel 181 and a deflector wheel 183situated respectively upstream and downstream from the ends 122, 124 ofthe support plate 120, and beneath the plane thereof. The belt 180 isguided by a curved horizontal slideway 188 (FIG. 15) along its returnpath between the reels 181 and 183, passing under the pipe 186.Similarly, the belt 190 passes over a drive wheel 191 and a deflectorwheel 193 situated upstream and downstream from the ends 122 and 124 ofthe support plate 120, beneath the plane thereof. The belt 190 is guidedby a curved horizontal slideway 198 along its return path between thedrive and deflector wheels, passing beneath the pipe 196.

The drive wheels 181, 191 are coupled to respective motors 181 a and 191a so as to move the belts 180 and 190 in the slideways 182, 192synchronously with the yarns that are being moved on the support plate120. It should be observed that the bottom slideways 188, 198 aredisposed substantially parallel to and vertically beneath the topslideways 182, 192. Thus, under the combined effect of the belts 180 and190 advancing and the yarn guides 280 being driven, each transverse yarn104 follows a zigzag path between the top strands of the belts 180, 190,and each time it reverses directly it is held pressed onto one of thebelts 180, 190 by the suction that is established in the slideways 182,192.

In a variant embodiment (FIG. 17), each transverse yarn 104 is held oneither side of the support plate 120 by means of pegs such as 195carried by the belts 180, 190. At each of its stroke, each yarn guide280 is guided to a reversal point situated slightly beyond the belt suchthat by the belt advancing the transverse yarn is caused to make a turnaround a peg carried by the belt. Each transverse yarn is thus held bythe pegs without any need for suction, such that the slideways 182, 192do not have any slots or holes and there is no need for a vacuum source.

In the above, it is assumed that a stationary support plate is used thatis in the form of a annular sector and that has a smooth surface.

In a variant, it is possible to use a rotary support plate 126 having atop portion in the form of a brush having rigid bristles 128, as shownin FIG. 18, the devices 100, 200, and 300 for lapping the transversesheet, for depositing the circumferential longitudinal sheet, and forassembling the two sheets together being, for example, the same as thosedescribed with reference FIGS. 1 to 3 and 7, 8.

The plate 126 forms a complete annulus which is rotated together withthe rings 130, 140, e.g. being secured thereto. The rigid bristles 128provide effective retention of the longitudinal yarns 204 so that thelongitudinal sheet can be deposited onto the support plate 124 prior tothe transverse sheet without any fear of the longitudinal yarns movingradially prior to the sheets being assembled together. In addition, therigid bristles 128 allow the needles to penetrate without damage to therotary support if the sheets are assembled together by needling.

At the outlet from the assembly device 300, the helical two-dimensionalsheet 402 is separated from the support plate 126 in an upward directionand it is removed laterally away from the support plate by being takenup by conical rollers (not shown).

It should be observed that the rings 130 and 140 could be omitted if therigid bristles 128 of the plate 126 are capable of effectively holdingthe yarns 104 of the transverse sheet once they have been lapped. Thiscan be the case when the yarns 104 are lapped radially while also beingmoved vertically at each end of the radial stroke so as to engage theyarns 104 in the rigid bristles 128 of the brush that forms the topportion of the plate 126.

It should also be observed that it is possible to envisage removing theresulting helical two-dimensional sheet laterally from the otherembodiments described (FIGS. 1 to 16) instead of collecting the sheet ina lower annular drum. The stationary support plate 120 in those otherembodiments could then be constituted by a complete annulus.

1. A method of making a helical two-dimensional fiber sheet, the methodcomprising the following steps: bringing at least one transverse fibersheet and lapping it while guiding it in a substantially radialdirection along a path in alternating directions between inner and outercircumferential edges of the sheet, with the transverse sheet beingreversed at each end of its path, the width of the transverse sheetbeing narrowed between the outer circumferential edge and the innercircumferential edge; holding the transverse sheet as it is lapped;pulling a plurality of substantially mutually parallel yarns or tows toform a helical longitudinal sheet with the density per unit area of thelongitudinal sheet decreasing from its longitudinally outer edge to itslongitudinally inner edge; superposing the helical longitudinal andtransverse sheets and advancing them flat in continuous rotation;assembling together the lapped transverse sheet and the longitudinalsheet to form a helical two-dimensional sheet; and removing the helicaltwo-dimensional sheet formed in this way.
 2. A method according to claim1, wherein the longitudinal sheet is brought onto the lapped transversesheet immediately prior to the sheet being assembled together.
 3. Amethod according to claim 1, wherein the transverse sheet is formed by aplurality of yarns or tows.
 4. A method according to claim 1, whereinthe transverse sheet is formed by at least one spread tow.
 5. A methodaccording to claim 1, wherein, while the transverse sheet is beinglapped it is guided by passing over a guide so as to encourage narrowingof the sheet while the guide is moving from the outer edge towards theinner edge of the sheet, and vice versa.
 6. A method according to claim5, wherein the guide comprises two curved bars against which thetransverse sheet bears in alternation while the guide is being moved inone direction and in the opposite direction between the outer and inneredges of the sheet.
 7. A method according to claim 3, wherein, while thetransverse sheet is being lapped it is guided by passing over a guide soas to encourage narrowing of the sheet while the guide is moving fromthe outer edge towards the inner edge of the sheet, and vice versa, andwherein each yarn or tow is also guided between fixed guide elementsextending substantially radially between the outer and innercircumferential edges of the sheet.
 8. A method according to claim 4,wherein, while the transverse sheet is being lapped it is guided bypassing over a guide so as to encourage narrowing of the sheet while theguide is moving from the outer edge towards the inner edge of the sheet,and vice versa, and wherein the spread tow(s) are also guided betweentwo stationary guide elements extending substantially radially betweenthe outer and inner circumferential edges of the sheet.
 9. A methodaccording to claim 3, wherein each yarn or tow of the transverse sheetis guided by passing through a respective yarn guide that is movedbetween the outer and inner circumferential edges of the sheet.
 10. Amethod according to claim 1, wherein, after lapping, the transversesheet is held, where it reverses, on supports situated along the outerand inner edges of the sheet, which supports are moved synchronouslywith the advance of the lapped transverse sheet and of the longitudinalsheet.
 11. A method according to claim 10, wherein holding is providedby being sucked onto said supports.
 12. A method according to claim 10,wherein holding is provided by passing around pegs carried by saidsupports.
 13. A method according to claim 1, wherein the density perunit area of the longitudinal sheet is varied by using yarns or tows ofdifferent weights and/or by varying the spacing between the yarns ortows.
 14. A method according to claim 1, wherein the longitudinal yarnsor tows are pulled by passing them through a press comprising twoconical rollers pressing against each other.
 15. A method according toclaim 1, wherein the longitudinal sheet and the lapped transverse sheetare assembled together by needling.
 16. A method according to claim 1,wherein the longitudinal sheet and the lapped transverse sheet areassembled together by stitching using a bonding yarn.
 17. A methodaccording to claim 1, wherein the longitudinal sheet and the lappedtransverse sheet are assembled together by interposing hot-melt yarns.18. A method according to claim 1, wherein the transverse sheet and thelongitudinal sheet are fed onto a stationary annular support plate. 19.A method according to claim 18, wherein the support plate is in the formof a annular sector, having a downstream end situated downstream in theadvance direction from an assembly zone in which the longitudinal andtransverse sheets are assembled together, and the helicaltwo-dimensional sheet is removed at an outlet from the annular supportplate situated at its downstream end.
 20. A method according to claim19, wherein the helical two-dimensional sheet is wound helically as flatsuperposed turns in a rotary annular storage drum situated beneath theannular support plate and having substantially the same axis as thesupport plate.
 21. A method according to claim 1, wherein the transverseand longitudinal sheets are fed onto a rotary annular support plate. 22.A method according to claim 1, wherein the helical two-dimensional sheetis removed laterally from the annular support plate.
 23. An installationfor fabricating a helical two-dimensional fiber sheet, the installationcomprising: an annular support plate; a feed and transverse lappingdevice for moving a fiber sheet transversely along a back-and-forth pathfrom one side to the other of the annular support plate with thetransverse sheet being reversed at each end of the path and with thesheet being guided in a substantially radial direction; means forholding the lapped transverse sheet; a device for pulling a set of yarnsor tows to form a helical longitudinal sheet and for feeding it onto theannular support plate; a device for assembling together the lappedtransverse sheet and the longitudinal sheet to form a helicaltwo-dimensional sheet; means for continuously advancing the lappedtransverse sheet and the longitudinal sheet in flat rotation on theannular support plate; and means for removing the helicaltwo-dimensional sheet after the longitudinal and transverse sheets havebeen assembled together.
 24. An installation according to claim 23,wherein the device for feeding and lapping the transverse sheetcomprises a guide over which the transverse sheet passes, and means fordriving the guide in reciprocating motion along a substantially radialpath between the sides of the annular support plate, the guide beingmade in such a manner as to encourage narrowing of the transverse sheetwhile the guide is moving from the outside of the annular plate towardsthe inside, and vice versa.
 25. An installation according to claim 24,wherein the guide comprises two curved bars against which the transversesheet bears in alternation when the guide is moved in one direction andin the other direction between the outer and inner sides of the annularplate.
 26. An installation according to claim 24, wherein, in order tofeed and lap a transverse sheet formed by a plurality of transverseyarns or tows, the feeding and lapping device further comprises aplurality of stationary guide elements disposed radially between theouter and inner sides of the annular plate and co-operating with thetransverse yarns or tows to guide each of them on its path between theouter side and the inner side of the annular support plate.
 27. Aninstallation according to claim 24, wherein, in order to feed and lap atransverse sheet formed by at least one spread tow, the feeding andlapping device further comprises two stationary guide elements disposedradially between the outer and inner sides of the annular support plate,and between which the transverse sheet is guided on its path between theouter side and the inner side of the annular support plate.
 28. Aninstallation according to claim 23, wherein, in order to feed and lap atransverse sheet formed by a plurality of transverse yarns or tows, thefeeding and lapping device comprises a plurality of yarn guides eachassociated with a respective transverse yarn or tow, and means fordisplacing the yarn guides back and forth along substantially radialpaths between the outer and inner sides of the annular support plate.29. An installation according to claim 23, wherein the means for holdingthe lapped transverse sheet comprise supports in the form of bands orrings situated on either side of the annular support plate, holdingmeans for holding the transverse sheet on said support where the sheetreverses, and means for driving said supports synchronously with theadvance means.
 30. An installation according to claim 29, wherein theholding means comprise a suction chamber associated with the supports inthe form of bands or rings in order to hold the transverse sheetthereagainst by suction.
 31. An installation according to claim 29,wherein the holding means comprise pegs carried by supports in the formof bands, so as to enable the transverse sheet to be reversed around thepegs.
 32. An installation according to claim 23, wherein the device forpulling the longitudinal sheet comprises a press formed by two conicalrollers with the yarns or tows forming the longitudinal sheet passingbetween them.
 33. An installation according to claim 23, wherein thedevice for assembling together the longitudinal sheet and the lappedtransverse sheet is a needling device comprising at least one needlinghead and extending over an annular sector above the annular supportplate.
 34. An installation according to claim 33, wherein the annularsupport is stationary and is provided with perforations in register withthe needles of the needling device.
 35. An installation according toclaim 23, wherein the device for assembling the longitudinal sheet andthe lapped transverse sheet together comprise at least one stitchinghead for assembling the sheets together by means of a bonding yarn. 36.An installation according to claim 23, wherein the advance meanscomprise drive means for driving the helical two-dimensional sheet inthe advance direction, the drive means being located downstream from theassembly device.
 37. An installation according to claim 23, wherein theannular support plate is stationary and extends over an annular sectorhaving a downstream end in the advance direction of the longitudinalsheet and the lapped transverse sheet, said downstream end beingsituated downstream from the device for assembling the sheets together.38. An installation according to claim 37, wherein the means forremoving the helical two-dimensional sheet comprise an annular drumsituated beneath the annular support plate and having substantially thesame axis as the support plate, and means for driving the annular drumsynchronously with the advance means so that the helical two-dimensionalsheet leaving the annular support plate from its downstream end iscontinuously collected and wound in the drum.
 39. An installationaccording to claim 23, wherein the annular support plate is a rotaryplate.
 40. An installation according to claim 39, wherein the annularsupport plate has a top portion forming a brush with rigid bristles.